This invention relates to off-road tires, more specifically, a preferred embodiment of this invention relates to a pneumatic all-terrain vehicle tire.
As used in this patent the term off-the road tires means pneumatic tires that have a primary use or working surface condition that is not on a paved road. Such tires include earthmover, agricultural tires, lawn and garden tires, and all-terrain vehicles tires, including, but not limited to off-road dirt bike tires and ATV tires.
Of particular interest are tires that have low operating pressures and minimal belt reinforcements. Tires in this class include farm tires or ATV tires. ATV tires generally operate at less than 10 psi and often times have no belt reinforcing structure.
All-terrain vehicles are relatively lightweight with a relatively low center of gravity. Early three wheel versions had knobby tires having small square block elements and a relatively shallow tread depth.
Later versions of xe2x80x9cQuad runnersxe2x80x9d or 4-wheel type ATV""s were developed and have been more widely accepted due to their improved stability. Horsepower increases and improvements in both vehicle suspension and chassis has resulted in vehicles capable of relatively high speed and much greater load carrying capacity.
The tires used on these vehicles are operated at very low pressures in the 0.7 bar 10 psi or less range. The tires are very wide with relatively large air chambers, which assist in absorbing shock and vibration. The tires generally have nominal rim diameters of 36 cm 14 inches or less and overall diameters of 69 cm 27 inches or less.
Often the rear tires are of a slightly larger size than the more lightly loaded front tires.
In aggressive off-the-road applications, the tires must have a very open tread pattern that employs elongated lugs which provide effective straight-line or drawbar traction to enable the vehicle to climb hilly and rough terrain, as shown in U.S. Design Pat. No. 308,038. Additionally, the tread must provide excellent lateral traction for vehicle stability during turning maneuvers as is disclosed in U.S. Pat. No. 5,259,429.
The tire disclosed in that patent employs a repeating pattern of long, intermediate length and short lugs arranged to provide improved traction. The arrangement of these lugs is such that each lug wraps completely over the tread shoulder portion. The lugs are also circumferentially relatively closely spaced such that numerous lugs are in the footprint of the tire at any one time. The tire made according to this prior art invention is considered one of the best mud tires in its class according to its manufacturer.
In wet soils with heavy clay content there is a tendency for the tread to pack with mud between the elongated lugs. The circumferential space between the adjacent lugs is commonly referred to as a soil discharge channel. The channels extend generally from the centerplane of the tread axially outwardly over the tread shoulder. Once this area is packed with mud, the tread effectively looses its ability to provide any traction. This is because the lugs are buried in the packed mud giving the tire the appearance of a slick or racing tread devoid of grooves.
For the very reasons these tires have such good traction capabilities, they exhibit a relatively high potential for stubble damage in the area of the inner tread surface. This thin inner tread surface lies between the tread lugs and sharp objects such as the rocks, sticks, thorns or roots can penetrate this undertread causing the tire to deflate.
It is an object of the present invention to minimize this type of tire damage without increasing tire weight or losing tire performance.
A further objective of the present invention is to maintain the tread pattern, which is self-cleaning in wet clay soil conditions.
It is still a further objective that the tread design maintain its good handling and traction performance on firm soils without any penalties in tire weight.
An off-road tire having a casing and a tread radially outward of the casing is disclosed. The tread has an inner tread and a plurality of lugs extending radially outward from the inner tread.
The tread has a plurality of elongated pads, each elongated pad is oriented in a direction substantially parallel to the centerlines of circumferentially adjacent lugs. Each pad has a base width  as measured from the inner tread and a radial height X also being measured from the inner tread.  is at least three times greater than X. Each longitudinal sidewall has a slope of 30xc2x0 or less as measured from the inner tread surface, preferably about 20xc2x0 or less. The radial height is less than 0.2 inches (5 mm).
The elongated pads each have a pair of tapered ends extending across the sides. The tapered ends are inclined at an angle of about 45xc2x0 or less relative to the inner tread surface.
In some cases whether there is a substantial circumferential space between adjacent lugs, it may be desirable to further include a radially outer or flat surface interposed between the pair of sloped longitudinal sides.
In the most preferred embodiment of the invention the off-road tire is an ATV tire. This ATV tire has the tread having the lugs arranged in an array of lugs oriented in a repeating directional pattern. The arrays are in rows around the circumference of the tread. A first array of lugs extends angularly from an axially inner end adjacent the centerplane (EP) of the tread toward a first lateral edge terminating an axially outer end. A second array of tread lugs extends angularly from an axially inner end adjacent the centerplane of the tread towards the second lateral edge terminating at an axially outer end. The space between each pair of first or second circumferentially adjacent arrays of lugs defines a soil discharge channel. Each pair of first or each pair of second arrays of lugs has the elongated pad located within the soil discharge channel and interposed between circumferentially adjacent arrays. The elongated pad is inclined in a direction similar to the inclination of the pairs of respective arrays.
Preferably the elongated pad interposed between circumferentially adjacent pairs of arrays is located substantially equal distance between centerlines of adjacent arrays. Each array of lugs has at least one circumferentially extending open channel between a pair of lugs within each array. At least one open channel intersects the soil discharge channel. It is believed desirable that the elongated pads have a length L of at least 35% of the tread arc width. Preferably the elongated pad extends from an axially inner end adjacent the equatorial plane outward to a lateral end covering substantially all of the soil discharge channels length.
The all terrain vehicle tire of the present invention preferably has a net-to-gross ratio of the tread as measured between the lateral edges around the entire circumference of the tread of less than 35%.
xe2x80x9cAll-terrain Vehicle ATVxe2x80x9d is any motorized off-highway vehicle 50 inches 1270 mm or less in overall width, with an unladen dry weight of 600 lbs. 275 kg or less, designed to travel on four or more low pressure tires, having a seat designed to be straddled by the operator and handlebars for steering control, and intended for use by a single operator and no passenger. Width and weight shall be exclusive of accessories and optional equipment. ATV""s are subdivided into four categories as follows:
Category G General Use Model ATV: An ATV intended for general recreational and utility use;
Category S Sport Model ATV: An ATV intended for recreational use by experienced operators only;
Category U Utility Model ATV: An ATV intended primarily for utility use.
Category Y Youth Model ATV: An ATV intended for recreational off-road use under adult supervision by operators under age 16. Youth model ATV""s can further be categorized as follows:
Category Y-6 ATV: A Category Y-6 ATV is a youth model ATV which is intended for use by children age 6 and older.
Category Y-12 ATV: A Category Y-12 ATV is a youth model ATV which is intended for use by children age 12 and older.
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of its section height to its section width.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBelt or Breaker Structurexe2x80x9d or xe2x80x9cReinforcing Belts or Breakersxe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17xc2x0 to 35xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cBias Ply Tirexe2x80x9d means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about a 25-65xc2x0 angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers.
xe2x80x9cCarcassxe2x80x9d means a laminate of tire ply material and other tire components, excluding the tread and any belt reinforcements, these additional components may be added to the carcass prior to its being vulcanized to create the molded tire.
xe2x80x9cEquatorial Plane EPxe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cInnerxe2x80x9d means toward the inside of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cOuterxe2x80x9d means toward the tire""s exterior.
xe2x80x9cPneumatic tirexe2x80x9d means a laminated mechanical device of generally toroidal shape usually an open-torus having beads and a tread and made of rubber, chemicals, fabric and steel or other materials. When mounted on the wheel of a motor vehicle, the tire through its tread provides traction and contains the fluid that sustains the vehicle load.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial Ply Tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65xc2x0 and 90xc2x0 with respect to the equatorial plane of the tire.
xe2x80x9cSection Heightxe2x80x9d SH means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection Widthxe2x80x9d SW means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.
xe2x80x9cSidewallxe2x80x9d means that portion of a tire between the tread and the bead.
xe2x80x9cTreadxe2x80x9d means a molded rubber component which when, bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.
xe2x80x9cTread Width or Tread Arc Widthxe2x80x9d means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.